void added inline comments.
================
Comment at: clang/test/Analysis/uninit-asm-goto.cpp:16
+ if (x < 42)
+ asm volatile goto("testl %0, %0; testl %1, %2; jne %l3" : "+S"(x), "+D"(y)
: "r"(x) :: indirect_1, indirect_2);
+ else
----------------
nickdesaulniers wrote:
> I wonder if it's straight forward to make this a "maybe uninitialized"
> warning, instead of "is uninitialized?" Consider the inline asm:
>
> ```
> asm volatile goto("ja %l1; mov %0, 42" : "=r"(foo) ::: bar);
> ```
> Since we can't introspect the inline asm, we're not sure whether `foo` gets
> initialized by the asm or not (as the asm could transfer control flow back to
> the C label before any assignments to the output). Telling the user it's
> definitely uninitialized is technically correct in this case, but definitely
> incorrect for:
>
> ```
> asm volatile goto("mov %0, 42; ja %l1;" : "=r"(foo) ::: bar);
> ```
The back end doesn't know how to generate code for a use in the indirect
branches. It's really complicated and may result in code that doesn't actually
work. I don't want to give off the impression that the code may work in these
cases, because it would be essentially working by accident.
================
Comment at: clang/test/Analysis/uninit-asm-goto.cpp:38
+ return 0;
+}
----------------
nickdesaulniers wrote:
> Are we able to catch backwards branches from `asm goto`? (if so, would you
> mind please added that as an additional unit test).
>
> ```
> int foo;
> goto 1;
> 2:
> return foo; // should warn?
> 1:
> asm goto ("": "=r"(foo):::2);
> return foo;
> ```
Yes, we should be able to warn about this. I added a testcase.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D71314/new/
https://reviews.llvm.org/D71314
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